Implements issue #1522. The agents plan list command now displays:
- Table with spec-required columns: ID, Phase, State, Action, Project, Elapsed
- Filters panel (shown when any filter is active)
- Summary panel (always shown) with Total, Processing, Completed, Errored counts
- Success message: ✓ OK N plan(s) listed
Removed non-spec columns: Name, Profile, Invariants
Added Elapsed column showing time since plan creation in HH:MM:SS format